Psychedelic drugs reopen critical windows of brain development and learning in adult mice.
During these 鈥渃ritical periods鈥�, the brain is highly plastic and capable of learning specific skills such as language. Once this window closes, it is nearly impossible to acquire certain abilities. For instance, children who aren鈥檛 exposed to language in their first year of life may never fully grasp sentence structure.
Previous research has shown that MDMA reopens a critical period of social learning in adult mice. So, at Johns Hopkins University in Maryland and his colleagues tested other psychedelic drugs to see if they have the same effect.
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They injected adult mice with LSD, psilocybin, ketamine or ibogaine 鈥� a psychedelic substance produced by the iboga plant found in West Africa. The doses of each drug were high enough to induce a psychedelic effect, and mice injected with saline served as controls. All the mice underwent a test that assesses preference for socialising two days before and two days after the injections.
In this test, a mouse spends 30 minutes exploring a cage with two compartments. The researchers then confine the mouse to one side with other mice for a day. On the second day, the mouse is isolated in the second compartment without the other mice. Finally, the mouse is again allowed to roam the entire cage for 30 minutes.
Previous experiments have shown that young mice spend most of this half hour on the side they associate with social interaction, whereas adult mice do not, says Sawyer. This is called social reward learning, a critical period in adolescence where mice find socialisation rewarding. While adult mice still enjoy socialising, it is not rewarding enough to condition their behaviour, says Sawyer.
Before the injections, all the mice spent roughly equal amounts of time on each side. This remained true for mice in the saline group during the second test. However, those given LSD, psilocybin and ketamine spent, on average, about 20 per cent more time on the side they associated with socialisation, and mice given ibogaine spent about 15 per cent more time on this side. Sawyer says this suggests these psychedelic drugs can reopen the critical period of social reward learning in mice.
鈥淭he idea you might be able to reopen a critical period could be helpful for all kinds of medical issues, injuries and development disorders,鈥� says Sawyer, who presented these findings on 14 November at the Society for Neuroscience annual meeting in San Diego, California.
However, it is unclear if these results will translate to humans, says at the University of Copenhagen in Denmark.
We also don鈥檛 know if psychedelics can reopen other critical periods such as the period after a stroke where motor skills can be regained, says Sawyer.
The mechanism by which psychedelics open the social reward learning critical period is still unclear. Sawyer believes it could have to do with these drugs鈥� ability to induce altered states of consciousness. 鈥淚t might actually be that those subjective experiences are what a reopening of a critical period feels like,鈥� he says.
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